Semiconductor integrated circuit chips are usually encapsulated in a protective package made of plastic, metal, or ceramic material. The package is hermetically sealed to insulate the semiconductor chip from the effects of temperature extremes, humidity, and unintentional electrical contacts. The package has a plurality of conductive leads protruding from the encapsulation material for connecting to external devices on a printed circuit board. Various types of semiconductor packages are commonly used in the art, including sealed metal cans, plastic and ceramic dual-inline packages, small-outlining packages, and various flat packages.
Most semiconductor packages contain only one semiconductor chip per package. There is a need to increase the density of a semiconductor package to include two or more chips in one package. A high density package having multiple chips would increase the component density on a printed circuit board. Such a high density semiconductor package also would maximize space utilization on a printed circuit board and further increase the number of active elements on the printed circuit board. Currently, thin vertical packages are used to increase component density on a printed circuit board. See, e.g., U.S. Pat. No. 4,975,763, entitled "Edge-mounted, Surface-mount Package For Semiconductor Integrated Circuit Devices," issued Dec. 4, 1990 to Boudouin, et al. By mounting the thin package vertically, a greater number of packages can be accommodated on a printed circuit board.
In the prior art, component density on a printed circuit board may be increased by using a chip module containing multiple single chip packages. An example of such a chip module is the Single inline Memory Module (SIMM). However, SIMM packages are bulky and do not significantly reduce the amount of space required. With respect to encapsulating multiple chips in one package, U.S. Pat. No. 5,014,112, entitled "Semiconductor Integrated Circuit Device Having Mirror Image Circuit Bars Bonded On Opposite Sides Of A Lead Frame," issued May 7, 1991, to Gelsomini, discloses a semiconductor package having two identical semiconductor chips mounted on a single lead frame. However, a package having one lead frame only provides a limited number of leads. In certain applications, semiconductor packages having more leads are required. For example, high density memory chips require more leads that currently available in a single lead frame. Therefore, a need has arisen for semiconductor packages encapsulating a plurality of semiconductor chips and having at least two rows of conductive leads.